The project, which was announced by Dionne at the Cannes Film Festival on Thursday (12May16) will also star Lady Gaga, Olympia Dukakis and Danny Glover.
Five-time Grammy Award winner Dionne, who is famed for her collaborations with songwriters Burt Bacharach and Hal David, praised LeToya as the ideal person to play her on screen.
"She is perfect and she has exactly the right look," Dionne tells The Hollywood Reporter. "She will bring out what is needed for this part."
The film will tell the story of Warwick's early career and rivalry with British singer Cilla Black, who will be played by Lady Gaga.
Cilla, who died in August last year (15), rose to stardom by recording one of Dionne's Bacharach and David penned hits, Anyone Who Had A Heart, for a U.K. audience.
The situation was reversed when Dionne released her own version of another Bacharach and David song, Alfie in 1967, which had been a U.K. hit for Cilla a year earlier.
Explaining why she regarded the Liverpudlian singer as her "nemesis", Dionne says, "Because she stole my music!"
Lethal Weapon star Danny Glover will play Dionne's father in the movie and Olympia will play her mentor Marlene Dietrich.
American filmmaker Mario Van Peebles is in talks to direct, with a script to be based on Dionne's autobiography My Life as I See It.
Other casting announcements made at the French film extravaganza this week (beg09May16) include The Hobbit star Martin Freeman receiving a role in Cargo, a zombie thriller, and Fifty Shades of Grey actress Dakota Johnson joining Andrew Garfield in Under the Silver Lake, a neo-noir flick to be directed by It Follows filmmaker David Robert Mitchell.